tech.notes

2.19.2015

Open HTTP port 80 on CentOS

Got from here.

1. Look at the current iptables
# iptables --line -vnL
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination
1        0     0 ACCEPT     udp  --  virbr0 *       0.0.0.0/0            0.0.0.0/0           udp dpt:53
2        0     0 ACCEPT     tcp  --  virbr0 *       0.0.0.0/0            0.0.0.0/0           tcp dpt:53
3        0     0 ACCEPT     udp  --  virbr0 *       0.0.0.0/0            0.0.0.0/0           udp dpt:67
4        0     0 ACCEPT     tcp  --  virbr0 *       0.0.0.0/0            0.0.0.0/0           tcp dpt:67
5     195K  212M ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED
6        3   252 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0
7       74  5440 ACCEPT     all  --  lo     *       0.0.0.0/0            0.0.0.0/0
8       16   864 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           state NEW tcp dpt:22
9     170K   39M REJECT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           reject-with icmp-host-prohibited

2. Inject rule, as long as it's before the REJECT line
# iptables -I INPUT 5 -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT

3. Save
# service iptables save

4. Add httpd_t to the list of permissive domains (So we don't need to turn off selinux)
# yum install policycoreutils-python
# semanage permissive -a httpd_t

Perl specific installs for Centos 6.6

1. Enable RPMForge Repository

# wget http://packages.sw.be/rpmforge-release/rpmforge-release-0.5.3-1.el6.rf.x86_64.rpm
# rpm -Uvh rpmforge-release-0.5.3-1.el6.rf.x86_64.rpm
# rpm --import http://dag.wieers.com/rpm/packages/RPM-GPG-KEY.dag.txt

2. Install perl installs

MANUAL:
1. Dependency of Net::SSH::Perl
# wget http://download.opensuse.org/repositories/home:/csbuild:/Perl/CentOS_CentOS-6/x86_64/perl-Math-GMP-2.04-2.5.x86_64.rpm
# rpm -Uvh perl-Math-GMP-2.04-2.5.x86_64.rpm

2. Dependency of gnuplot for Chart::Graph::Gnuplot
# wget http://www.my-guides.net/en/images/stories/fedora12/msttcore-fonts-2.0-3.noarch.rpm
# rpm -Uvh msttcore-fonts-2.0-3.noarch.rpm

YUM:
# yum install perl-Math-BigInt-GMP
# yum install perl-Math-Pari
# yum install perl-Archive-Zip
# yum install perl-Chart
# yum install perl-DBI
# yum install perl-DBD-MySQL
# yum install perl-Data-Compare
# yum install perl-Date-Manip
# yum install perl-JSON
# yum install perl-Net-Telnet
# yum install perl-NetAddr-IP
# yum install perl-Statistics-Descriptive
# yum install perl-Text-Table
# yum install perl-XML-Simple
# yum install perl-XML-Writer
# yum install gnuplot

CPAN:
# cpan Data::Diff
# cpan HTML::TextToHTML
# cpan XML::SemanticDiff
# cpan Chart::Graph - this didn't install

Force installed:
cpan[1]> force install Net::Telnet::Brcd

2.13.2015

Install different versions of Perl on Linux using Perlbrew

Got from here and here. What is perlbrew.

1. Install perfbrew
$ curl -kL http://install.perlbrew.pl | bash

2. Modify .bashrc and add:
source ~/perl5/perlbrew/etc/bashrc

3. Initialize
$ perlbrew init

4. Select mirror
$ perlbrew mirror

5. See what's available
$ perlbrew available
  perl-5.20.1
  perl-5.18.4
  perl-5.16.3
  perl-5.14.4

6. Install perls
$ perlbrew install perl-5.20.1  # did not work for Centos 6.5
$ perlbrew --notest install perl-5.20.1

7. See what were installed
$ perlbrew list

8. Swith to an installation and set it as default
$ perlbrew switch perl-5.20.1

9. Temporarily use another version only in current shell.
$ perlbrew use perl-5.20.1
$ perl -v

10. Or turn it off completely. Useful when you messed up too deep. Or want to go back to the system Perl.
$ perlbrew off

11. Use 'switch' command to turn it back on.
$ perlbrew switch perl-5.20.1

12. Exec something with all perlbrew-ed perls
$ perlbrew exec -- perl -E 'say $]'

13. Install cpanm
$ perlbrew install-cpanm

14. Install cpan modules
$ cpanm install File::Copy::Recursive XML::Simple etc

2.07.2015

While reading RubyMonk tutorials

1. Truthiness of objects in Ruby
Only objects false and nil equates to false. Every other object like say 1, 0, "" are all evaluated to be true.

2. Use break in infinite loops

loop do
  monk.meditate
  break if monk.nirvana?
end

3. Append to an array, use << operator

[1, 2, 3, 4, 5] << 'woot'
[1, 2, 3, 4, 5, "woot"]

4. Filter elements of an array, use 'select'

names = ['rock', 'paper', 'scissors', 'lizard', 'spock']
names.select { |word| word.length > 5 }

5. Delete elements of an array, use 'delete_if'

[1,2,3,4,5,6,7,8,9].delete_if { |i| i % 2 == 0 }

6. Methods are themselves objects, and responds using 'call'

next_method_object = 1.method("next")
puts next_method_object.call

7. Beware of shallow object copies, to do a deep copy use Marshal

new_job = Marshal.load(Marshal.dump(job))

8. Use heredoc for convenient multiline strings. The dash ignores spaces before placeholder. The gsub takes care of removing spaces at beginning of each line.

def long_message
  puts <<-EOT.gsub(/^\s*/, '')
    Here goes a very long message...
    Sincerely,
    Dr. Foobear
  EOT
end

7. Use 'send' when testing private methods

# obj.send(:method_name, args)
@parser.send(:running?, test_strings)

1.21.2015

Use iperf to measure network link bandwidth

Nice writeup on how to use iperf. Another example, writeup.

1. Install iperf
$ sudo yum install iperf

2. Start server on another system:
$ iperf -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
------------------------------------------------------------
[  4] local 10.1.1.1 port 5001 connected with 10.0.0.1 port 46699
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.3 sec   107 MBytes  87.7 Mbits/sec

3. Start client from your system specifying server ip:
$ iperf -c 10.1.1.1
------------------------------------------------------------
Client connecting to 10.1.1.1, TCP port 5001
TCP window size: 85.0 KByte (default)
------------------------------------------------------------
[  3] local 10.0.0.1 port 46699 connected with 10.1.1.1 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.1 sec   107 MBytes  89.0 Mbits/sec

4. Use options, e.g., -t duration, -i interval between measurements
$ iperf -c 10.1.1.1 -t 20 -i 2
------------------------------------------------------------
Client connecting to 10.1.1.1, TCP port 5001
TCP window size: 85.0 KByte (default)
------------------------------------------------------------
[  3] local 10.0.0.1 port 46761 connected with 10.1.1.1 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0- 2.0 sec  17.6 MBytes  73.9 Mbits/sec
[  3]  2.0- 4.0 sec  22.5 MBytes  94.4 Mbits/sec
[  3]  4.0- 6.0 sec  21.2 MBytes  89.1 Mbits/sec
[  3]  6.0- 8.0 sec  22.6 MBytes  94.9 Mbits/sec
[  3]  8.0-10.0 sec  22.5 MBytes  94.4 Mbits/sec
[  3] 10.0-12.0 sec  21.2 MBytes  89.1 Mbits/sec
[  3] 12.0-14.0 sec  22.6 MBytes  94.9 Mbits/sec
[  3] 14.0-16.0 sec  22.5 MBytes  94.4 Mbits/sec
[  3] 16.0-18.0 sec  21.2 MBytes  89.1 Mbits/sec
[  3] 18.0-20.0 sec  22.5 MBytes  94.4 Mbits/sec
[  3]  0.0-20.1 sec   217 MBytes  90.6 Mbits/sec

Just want to take note: Bandwidth vs Throughput

Bandwidth : Refers how fast a device can send data over a single communication channel.
Throughput: Refers how fast a device is actually sending data over the communication channel.

1.20.2015

Network 2 ubuntu systems via crossover cable

Got from here.

1. Pick one of the computers to be the server. If one computer has a connection to the Internet use that as the server.

2. On the server click the network indicator and chose "Edit Connections...". Select the Ethernet connection then click the "Edit..." button. Go to the IPv4 tab and change "Method" from "Automatic (DHCP)" to "Shared to other computers".

3. Connect the two computers together using an Ethernet cable. The second computer will get assigned an IP address from the server and get access to the Internet.

If you have old hardware you may need to make sure the Ethernet cable is a crossover cable. Modern hardware automatically does the crossover.

==============================================
hostname:mango, os:Ubuntu 14.10 Utopic Unicorn
==============================================
ASRock Z97 Extreme6 LGA 1150 Intel Z97 HDMI SATA 6Gb/s USB 3.0 ATX Intel Motherboard
Intel Core i7-4790 Haswell Quad-Core 3.6GHz LGA 1150 84W Desktop Processor Intel HD Graphics 4600
Team Xtreme 16GB (2 x 8GB) 240-Pin DDR3 SDRAM DDR3 2400 Desktop Memory
OCZ ARC 100 ARC100-25SAT3-240G 2.5" 240GB SATA III MLC Internal Solid State Drive
Western Digital WD Blue WD10EZEX 1TB 7200 RPM 64MB Cache SATA 6.0Gb/s 3.5" Internal Hard Drive
ENERMAX Ostrog GT ECA3280A-BR Black / Red Steel / Plastic ATX Mid Tower Computer Case

Install and setup Samba on Ubuntu

Got from here.

1. Install samba
$ sudo apt-get update
$ sudo apt-get install samba

2. Set a password for samba user
$ sudo smbpasswd -a samdc
New SMB password:
Retype new SMB password:
Added user samdc.

3. Create a directory to be shared
$ sudo mkdir /data1/staging

4. Make sure user has access
$ sudo chown samdc:samdc /data1/staging

5. Make a backup copy of smb.conf
$ cp /etc/samba/smb.conf ~

6. Edit smb.conf
$ sudo vi /etc/samba/smb.conf
Add this to the very end of the file:
[staging]
path = /data1/staging
available = yes
valid users = samdc
read only = no
browseable = yes
public = yes
writable = yes

7. Restart samba
$ sudo service smbd restart

8. Check smb.conf for any syntax errors
$ testparm

9. To access network share
Linux:
smb://<HOST_IP_OR_NAME>/<folder_name>/
smb://10.42.0.1/staging/

Windows:
\\<HOST_IP_OR_NAME>\<folder_name>\
\\10.42.0.1\staging\